The present invention relates to an industrial robot wrist unit, comprising a wrist housing, which is intended to be detachably fixed to a distal end of a robot arm and in which there is pivotally mounted a tilt housing, which in turn supports a rotatably mounted turntable on which there can be mounted an external tool, first and second secondary drive shafts being rotatably mounted in the wrist housing, the first and second secondary drive shafts each having an input end which supports a gear for engagement with a respective drive gear on a respective primary drive shaft in the robot arm, the drive gears being disposed coaxial to each other and axially spaced, and where the first secondary drive shaft via a respective first gearing can rotate the turntable about a first axis and the second secondary drive shaft can, via a respective second gearing, pivot the tilt housing about a second axis, which crosses the first axis.
In a previously known wrist unit of the above mentioned type, the wrist housing comprises two halves, where each half has a through-hole for a respective secondary drive shaft. When assembled, the center axes of the holes for the secondary drive shafts in the housing halves, and thereby the center axis of the gears thereon, are disposed on diametrically opposite sides of the central coaxial driving gears on the primary drive shafts in the robot arm with which they are in engagement. In other words a straight line extends through the center axes of the secondary gears and the coaxial drive gears. This has made it difficult to adjust the clearance between the drive gears and their respective gears on the secondary drive shafts.